Regulation (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended	0 Months Ended	27 Months Ended	0 Months Ended	9 Months Ended	0 Months Ended			9 Months Ended		0 Months Ended						0 Months Ended
	Sep. 30, 2013	Sep. 30, 2013	May 01, 2012 2012 Texas Retail Rate Case	Sep. 30, 2011 2012 Texas Retail Rate Case	Sep. 07, 2013 PUCT MW	Sep. 30, 2013 PUCT	Oct. 30, 2013 NMPRC	Sep. 07, 2013 NMPRC MW	Nov. 21, 2012 NMPRC MW	Sep. 30, 2013 NMPRC	Oct. 29, 2013 NMPRC	Oct. 01, 2013 FERC	Sep. 30, 2013 FERC	Sep. 28, 2013 FERC	Jan. 31, 2013 FERC	Aug. 03, 2012 PUCT Docket No. 40622	Sep. 23, 2013 PUCT Docket No. 41803	Sep. 27, 2013 PUCT Docket No. 41852	Sep. 07, 2013 MPS To Caliente Transmission Line PUCT Docket No. 41360 kV	Sep. 07, 2013 MPS In & Out Transmission Line PUCT Docket No. 41359 kV	Sep. 07, 2013 Caliente - Coyote Transmission Line PUCT Docket No. 41359 kV	Sep. 07, 2013 MPS To Montwood Transmission Line PUCT Docket No. 41809 kV	Oct. 30, 2013 Nuclear Fuel Financing NMPRC	Sep. 30, 2013 Nuclear Fuel Financing FERC
Reconcilable Fuel Expense				$ 356.5
Reduction in Annual Nonfuel Base Rate			15
Reduction in Depreciation Expense			4.1
Return on Equity			10.125%
Number of years rate case expenses amortized			2 years
Increase (Decrease) In Fixed Fuel Factor																	16.9
Percent Increase (Decrease) In Fixed Fuel Factor																	12.20%
Fuel over and under materiality threshold percentage						4.00%
Refund Payments Authorized																6.6
Cost of Purchased Power																		545.3
Fuel Reconciliation Period																		45 months
Rewards Authorized By Regulator For Operations																		3.4
Number of Power Generation Units		2				2				2
Electric Capacity					88			88	50										115	115	115	115
Number Of Transmission Lines	3
Line of Credit Facility, Current Borrowing Capacity							400				300		400	300
Line of Credit Facility, Expiration Period							4 years					4 years
Debt Instrument, Face Amount							300						300										50	50
Refund Related to Dispute															$ 1.9
Effective FERC Approval Period												2 years